Low resistivity tire with silica-rich tread and at least one electrostatic discharge ring

Abstract

The tire of this invention has a silica-rich tread compound for excellent rolling resistance and tread wear properties. The tire is made to be conductive such that electrostatic charges on the vehicle can be quickly dissipated when the vehicle stops. An electrostatic discharge ring is located on at least one shoulder portion of the tire and has a relatively low volume resistivity, on the order of 100 megohm centimeter. The discharge ring is positioned to make contact with a conductive sidewall portion of the tire. The overall resistivity of the tire from the rim to the ground surface is made to be less than about 100 megohms.

Having described the embodiments of this invention in sufficient detail for those in the art, what is claimed is: 
     
       1. A radial pneumatic tire with a silica-rich tread which is capable of timely discharging the static electricity accumulated in a vehicle on which the tire is mounted, comprising: a toroidal carcass terminating at opposite bead regions of the tire which are adjacent a rim of the vehicle when the tire is mounted on the rim;   a belt package radially outward of a crown portion of the carcass, and a belt edge rubber portion at each lateral edge of said belt package;   a pair of spaced apart sidewall rubber portions each positioned axially outside a respective lateral portion of said carcass and extending radially inward from a respective belt edge to contact said rim when the tire is mounted on the rim;   a tread portion, having at least a 50 percent silica content by weight, positioned radially outward of said belt package for contacting a ground surface over a contact patch having a tread width and supporting said tire of the vehicle; and   at least one electrostatic discharge ring positioned at a lateral edge of said tread and axially inward of a respective sidewall portion and having a first edge located axially inward of a lateral edge of the tread width at a surface of the tread and a second edge located radially inward of said tread portion, wherein said at least one discharge ring provides a conductive path from the ground surface to a combination of a conductive belt edge rubber portion and a conductive sidewall rubber portion when the tire is in service.   
     
     
       2. The tire set forth in claim 1, wherein said at least one electrostatic discharge ring has a relatively constant thickness value in the range of about 0.2 millimeter to about 1.0 millimeter, said at least one discharge ring being formed into lateral grooves in said tread during the curing operation. 
     
     
       3. The tire set forth in claim 1, wherein the electrostatic discharge ring has a rubber volume resistivity value in a range of about 10 megohm centimeter to about 100 megohm centimeter. 
     
     
       4. The tire set forth in claim 1 wherein the conductive sidewall rubber portion as well as the conductive belt edge rubber portion have a rubber volume resistivity value of not more than about 100 megohm centimeter. 
     
     
       5. The tire set forth in claim 2, wherein a first distance that the first edge of said at least one discharge ring extends axially inward from the lateral edge of the tread width is at least 7 percent of the tread width at normal vehicle operating conditions of load and pressure when said tire is new. 
     
     
       6. The tire set forth in claim 5, wherein the first distance the first edge of said at least one discharge ring extends radially inward from the lateral edge of the tread width is such that each discharge ring over the contact patch having the tread width has at least 15 square millimeters of area at a surface of the tread during the life of the tread. 
     
     
       7. The tire set forth in claim 1, wherein a second distance the second edge of said at least one discharge ring extends radially inward is a distance from the tread of at least 3 millimeters and a distance from the radially outer edge of the conductive sidewall rubber portion of at least 20 millimeters. 
     
     
       8. The tire set forth in claim 1, wherein there are two electrostatic discharge rings each positioned at a respective lateral edge of said tread and having a relative constant thickness value in the range of about 0.2 millimeter to about 1.0 millimeter, said discharge rings being formed into lateral grooves of the tread during the tire's curing operation. 
     
     
       9. The tire set forth in claim 8, wherein the electrostatic discharge rings each have a rubber volume resistivity value in a range of about 10 megohm centimeter to about 100 megohm centimeter. 
     
     
       10. The tire set forth in claim 9, wherein a first distance the first edge of each discharge ring extends axially inward of a respective lateral edge of the tread width is at least 7 percent of the tread width at normal vehicle operating conditions of load and pressure when the tire is new. 
     
     
       11. The tire set forth in claim 10, wherein the first distance the first edge of each discharge ring extends axially inward of a respective lateral edge of the tread width is such that each discharge ring over the contact patch having the tread width has at least 15 square millimeters of area at a surface of the tread during the life of the tread. 
     
     
       12. The tire set forth in claim 9, wherein a second distance the second edge of each discharge ring extends radially inward is a distance from the tread of at least 3 millimeters and a distance from the radially outer edge of the respective conductive sidewall rubber portion of at least 20 millimeters, the respective conductive sidewall rubber portion having a volume resistivity of not more than about 100 megohm centimeter. 
     
     
       13. The tire set forth in claim 1, wherein the overall resistance of the tire from the rim to the ground surface when the tire is in service is not greater than about 100 megohms. 
     
     
       14. The tire set forth in claim 8, wherein the overall resistance of the tire from the rim to the ground surface when the tire is in service is not greater than about 100 megohms.